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United States Patent 0
discrete particles of incompletely foamed-up thermoplastic
organic polymers containing a volatile organic ?uid foam
ing agent and which polymer particles are normally sus
cepti‘ole to clumping into aggregates of a plurality of said
particles adhered to one another upon expanding by
heating. A further object is to provide a method and
agents for inhibiting or preventing the clumping of foam
3,086,885
NON-CLUMPIN’G FOAMABLE THERMOPLASTEQ
PQLYMER GRANULES AND METHGD 0F
MAKlNG
Alex K. .lahn, Midland, Mich, assignor to The Dow
Chemical Company, Midland, Mich, a corporation of
Delaware
‘ No Drawing. Filed Sept. 22, 1960, Ser. No. 57,616
'
5 Claims.
(Cl. 117-400)
Patented Apr. 23, 1963
2
1
'
3,086,885
1
able thermoplastic organic polymers upon being incom
pletely foamed-up, which agents are effective for said pur
10 pose, but do not inhibit or prevent the bonding together
of said incompletely foamed-up polymer particles upon
This invention concerns compositions consisting of
subsequent further expanding in a mold to produce a
granular or particulate foamable thermoplastic organic
cellular molded article. Other and related objects will
polymers having on the‘surfaces thereof watenrepellant
become apparent from the following description of the
non-clumping agents for inhibiting the formation of ag
.
gregates of said particles upon expanding the same by 15 invention.
According to the invention, the foregoing and related
heating to produce free-?owing incompletely foamed-up
polymer granules, and pertains to a method of making
objects are obtained by coating onto the surfaces of the
the same.
normally susceptible to clumping into aggregates of a
granules of a foarnable thermoplastic organic polymer
It is known to prepare foamable polystyrene or styrene
polymers by incorporating therewith a volatile organic 20 plurality of granules adhered to one another upon ex
panding by heating during an incompletely prefoaming
compound such as pentane, petroleum ether, per-chloro
treatment, a ?uid polysiloxane of the formula RZSiO
?uorocarbons, e.g. dichlorodi?uoromethane, dichloro
wherein R represents a radical of the group consisting of
the methyl and the phenyl radical and wherein at least 75
or mass of the polymer, preferably in particulate form, 25 percent of the total R radicals in the polysiloxane are
methyl radicals in amount corresponding to from about
in a porous mold to produce cellular or foamed articles
5 to about 500, preferably from 5 to 300, parts by weight
having a shape corresponding to that of the mold cavity.
of the polysiloxane per million parts by weight of the
In the making of molded articles, it is common practice
tetra?uoroethane, and the like, and to expand or foam
such thermoplastic organic polymers by heating a body
polymer.
to ‘fill or substantially ?ll a porous mold with a mass of
It is important that the polysiloxane be employed in
amounts within the range of from about 5 to 500 parts by
or incompletely foamed-up and still contain su?icient of
weight per million parts by weight of the'polymer, or
the volatile organic ?uid, ‘or raising agent, which upon
stated differently, in amounts corresponding to from
heating of the polymer to its softening point or above and
about 0.0005 to 0.0500 percent by weight of the polymer,
above the boiling point of the volatile organic ?uid re
sults in further expanding of the polymer granules in the 35 in order to obtain the improved free-?owing non-clump
ing prefoamed polymer granules, and to avoid the forma
mold and a pressing together and bonding of the particles,
tion of foamable or foamed polymer articles which have
because of the expansion, into 1a shaped cellular article.
an enhanced ?ammability.
In order to prepare, incompletely foamed-up small-parti
The polysiloxanes to be employed in the invention are
cled thermoplastic organic polymers from the solid poly
mer particles containing a ‘volatile organic ?uid raising 40 the ?uid, liquid to paste-like, benzene-soluble diorgano
polysiloxanes in which the siloxane units consist of units
agent, the polymer particles are heated above the soften
of the structural formula R2830‘ wherein R is a radical
ing point of the polymer for such a length of time that
selected from the group consisting of the methyl radical
only part of the foaming agent is used up or vaporized in
and the phenyl radical and ‘wherein at least 75 percent of
expanding or prefoaming the polymer particles. ‘ For ex
ample, polystyrene beads containing petroleum ether, 45 the total number of the R radicals in the polysiloxane
are methyl radicals. The polysiloxane can be one in
B.P. 30—46° C., can be incompletely foamed-up by im
which all of the siloXane units are (CH3)2SiO‘ or the
mersion in Water at 75° to 100° C. for about 3 to 10 min
sil-oxane may be a copolymer of dimethyl siloxane and a
utes, or by heating with steam at atmospheric pressure
minor proportion of the units: C6H5(CH3)SiO or
for a similarly short period of time, then cooling or al
lowing the prefoamed granules to cool to room tempera
the foama‘ble polymer granules which have been partially 30
(C6H5 ) 2SiO
ture or thereabout.
It has been observed, in preparing the incompletely
foamed-up polymer granules, that many of the polymer
granules are normally susceptible to clumping into ag
provided that the polysiloxane employed contains at least
gregates of a plurality of particles adhered to one another 55 75 percentof the total R radicals therein as methyl radi
cals. The polysiloxanes are preferably normally liquid
upon expanding by heating during the prefoarning treat
silicone ?uids such as are readily available on the open
market in the form of liquids per se or as solutions in
ment, and these aggregates are disadvantageous and un
desirable in subsequent use of the prefoamed granules in
organic solvents which are poor solvents for the polymer
the making of cellular articles having a desired shape.
Accordingly, it is a primary object of the invention to 60 or as aqueous emulsions of the same.
It is also important that the herein speci?ed polysilox
provide a method and agents for inhibiting or preventing
anes be employed in amounts corresponding to not more’
the clumping of foamable thermoplastic organic poly
mers upon incompletely foaming-up by heating, to pro
duce free-flowing prefoamed polymer granules. Another
object is to produce free-?owing compositions comprising
65
than about 500 parts by Weight per million parts by weight
of the polymer in order to avoid enhancing the ?ammabil
ity or burning rate of the foamed cellular product.
4
It has now been discovered that the applying of av poly
preferably with an aqueous emulsion or a solution of the
?uid polydiorganosiloxane, in the amount to uniformly
distribute the siloxane over the surfaces of the granules,
after which the granules are dried or allowed to dry in
air at room temperature or thereabout. Blending of the
polymer granules with the polysiloxane or an aqueous
emulsion thereof is also carried out at room temperature
or thereabout and at atmospheric or substantially atmos
siloxane coating to the surfaces of a foamable thermo
plastic organic polymer such as polystyrene or to a foam
able styrene polymer containing an organic bromide as
?ame-proo?ng agent, in amounts greater than ‘herein spec
i?ed, then foaming the polymer, for example by heating
in a porous mold, results in the ‘formation of a cellular
product which burns at an accelerated rate. It has fur
ther been discovered that the incorporating of the poly
siloxane throughout the foamable ?ame-proofed polymer
granules, even in ‘amounts within the range herein speci
?ed e.g., in amounts of 0.01 percent by weight or more,
then foaming of the polymer granules in a mold to pro
duce a cellular article, results in the making of a cellu
10
pheric pressure.
The invention is advantageously employed for the mak
ing of free-?owing compositions comprising discrete par
ticles of foamable thermoplastic organic polymers such as
?ammable alkenyl aromatic polymers, normally suscep
tible to clumping into aggregates of a plurality of said par
lar product which readily burns.
15 ticles upon expanding by heating to produce prefoamed
In contrast, the free-?owing compositions of the inven
or incompletely foamed-up particles, and which polymer
tion comprising discrete particles of a foamable thermo
particles contain intimately admixed therewith an organic
plastic organic polymer cont-aining a volatile organic ?uid
bromide as ?ame-proo?ng agent, which prefoamed and
foaming agent and normally susceptible to clumping into
free-?owing particles are suitable for use by expanding in
aggregates of a plurality of said particles adhered to one 20 a mold to produce cellular articles of a predetermined
another upon expanding by heating, are readily obtained
shape and which are ?ame-proof or resistant to burning.
by coating onto the surfaces of said polymer particles
The following examples illustrate ways in which the
from 0.0005 to 0.0500 percent by Weight of a ?uid polydi
principle of the invention has been applied, but are not
organosiloxane of the formula RgSiO wherein R is a radi
to be construed as limiting its scope.
cal selected from the group consisting of the methyl radi 25
cal and the phenyl radical and wherein at least 75 percent
EXAMPLE 1
of the total R radicals in the polysiloxane are methyl radi
"In each of a series of experiments ,a charge of foam
cals.
able polystyrene granules in the form of beads of sizes
The thermoplastic organic polymer to be employed can
be any normally solid organic polymer which is thermo 30 between 0.8 and 1.5 millimeters in diameter, and con
plastic and contains a volatile organic ?uid foaming agent
which is soluble in, but does not dissolve, the polymer.
The organic polymers are preferably alkenyl aromatic
polymers which contain in polymerized or interpolymer
taining 1.5 percent by weight of 1,2-dibromotetrachloro
ethane as self-extinguishing agent and about 6 percent by
weight of pentane as foaming agent, uniformly dispersed
throughout the beads, which beads were prepared by poly
ized form at least 50 percent by weight of at least one 35 merizing monomeric styrene containing the l,2ddibromo
tetrachloroethane and the pentane dissolved therein while
monoalkenyl aromatic compound having the general for
mula
suspended as droplets in an aqueous medium, was blended
R
with 3 percent by weight of a liquid‘ mixture consisting of
an emulsion of water and polydimethyl siloxane in
40 amount, based on one million parts by weight of the poly
styrene starting material, as stated in the following table.
wherein Ar represents an aroma-tic radical of the group
consisting of hydrocarbon and nuclear halohydrocarbon
After thorough blending of the polystyrene granules with
the polyadimethyl siloxane emulsion to uniformly dis
tribute the poly-dimethyl siloxane over the surfaces of the
of the group consisting of hydrogen and the methyl radi 45 beads, the beads were dried in air at room temperature.
cal. Examples of such alkenyl aromatic polymers are the
Portions of the dried beads were pre-foamed by heating
solid homopolymers and copolymers of styrene, vinyl~
in hot water at 95—l00° C. for a period of about three
toluene, vinylxylene, isopropyl styrene, tert.-butyl styrene,
minutes. A portion of the pre-foamed beads was placed
radicals of the benzene series and R represents a member
ethylvinylbenzene, chlorostyrene, dichlorostyrene, bromo
in the cavity of a porous mold to substantially ?ll the
styrene, ?uorostyrene, and the solid copolymers of one or
more of such monoalkenyl aromatic compounds with
mold cavity. The mold was closed and the beads were
heated therein with steam at temperatures between 100°
minor amounts of other readily copolymerizable ole?nic
compounds such as divinylbenzene, methylmethacrylate
and 110° C. to form a cellular body having the dimen
liquid such as a saturated aliphatic hydrocarbon contain
ing vfrom 4 to 7 carbon atoms in the molecule, e.g. butene,
the ?ammability or buming time for the foamed material.
The procedure for determining the burning time was to
sions 10 x 1'0 x 14 inches. Test pieces of 1A x 1 inch
or acrylonitrile.
cross section by 5 inches long were cut from the molded
The‘volatile organic ?uid foaming agent can be a gas or 55 cellular body. These test pieces were used to determine
pentane, hexane, heptane, or petroleum ether, having a
hold a test piece by one end in a horizontal position with
the l-inch dimension in a vertical plane, then hold a
tures below 95 ° C. at 760 millimeters absolute pressure 60 microburner having a 1-inch ?ame under the free end of
or perchloro?uorocarbons such as dichlorodifluorometh
the foam test piece until the foam is ignited, and imme
molecular weight of at least 58 and boiling at tempera
ane, trichloro?uoromethane, tri?uorochloromethane, di
diately remove the ?ame. The time after igniting of the
foam until it is self-extinguished is recorded and is herein
atures below 95° C. at 760 millimeters. Such volatile or
called the “SE-time.” Table I identi?es the experiments
ganic ?uids are usually employed in amounts correspond 65 and gives the proportion of poly-dimethyl siloxane, ex
ing to fro-m 0.05 to 0.4 gram molecular proportion of the
pressed as parts by weight per million parts by weight
chlorotetra?uoromethane and the like boiling at temper
volatile organic compound per 100 gramsof the polymer.
(ppm) of the foamable polystyrene starting material,
Methods of incorporating the foaming agents such as by
that was coated onto the surfaces of the polystyrene beads.
soaking or steeping in, polymerizing the monomers in ad
The table also gives the self-extinguishing time in
mixture with the volatile organic ?uid under pressure or 70 seconds determined for the foam prepared from the coated
of blending the, solid heat-plasti?ed polymer with the
beads. The SE-time reported in the table is an average
time for from 5 to -8 tests. No clumping of the surface
need not be discussed in detail.
coated beads occurred in the pre-foaming step carried out
In practice, the ‘foamable polymer granules in solid or
prior to the molding of the prefoamed beads into a cel
dense foam, ‘i.e. substantially non-foamed, are blended, 75 lular body in the porous mold.
volatile organic ?uid, under pressure are well known and
3,086,885
6
‘5
that were clumped together as agglomerates of a plurality
of beads and the percent of surface water adhered to the
beads.
Table 11
Table l _
Poly-di
Run No.
methyl Silox
SE-time,
seconds
ane, ppm.
Surface
Poly
dimethyl Clumps, water,
percent
percent
Siloxane,
Remarks
ppm.
a’:
H
OH
Com com
H03
come
Poor ?owing beads.
Pourable beads.
FrceD?owing
beads.
o.
i claim:
Burns 15
1. A free-?owing composition comprising discrete par
ticles of a foamab-le thermoplastic styrene polymer, nor
Similar results are obtained when an aqueous emulsion
mally susceptible to clumping into aggregates of a plu
of a liquid polysiloxane consisting of : (1) a copolymer
rality of said particles adhered to one another upon ex
of 90 percent by weight of dimethylsiloxane and 10 per
cent of diphenylsiloxane; (2) a copolymer of 50 percent
by weight of dimethylsiloxane and 50 percent of methyl
phenylsiloxane; and (3) a copolymer of 75 percent by
weight of dimethylsiloxane and 25 percent of diphenyl
siloxane, instead of the polydimethylsiloxane employed
panding by heating, and having on the surfaces of said
particles a coating consisting of from 0.0005 to 0.0500
percent by weight of a ?uid polysiloxane of the formula
R2SiO wherein R is a radical selected from the group con
sisting of the methyl and the phenyl radicals and wherein
at least 75 percent of the total R radicals in said poly
in the example, or when solutions of such polysiloxanes in 25 siloxane are methyl radicals.
pentane or hexane are used.
In contrast, polystyrene granules prepared by polym
2. A free-?owing composition comprising discrete par
ticles of a foamable thermoplastic styrene polymer, nor
mally susceptible to clumping into aggregates of a plu
erizing monomeric styrene containing a similar amount of
1,Z-dibromotetrachloroethane and pentane and 0.01 per 30 rality of said particles adhered to one another upon ex
panding by heating, and consisting essentially of a ther
cent by weight of poly-dimethylsiloxane dissolved therein,
in an aqueous suspension, when foamed to produce a cel
lular article and tested in the same manner, burned
moplastic alkenyl aromatic polymer containing in polym
?ercely.
one monoalkenyl aromatic compound having the general
erized form of at least 50 percent by weight of at least
EXAMPLE 2
35 formula:
In each of a series of experiments a charge of 20
pounds of polystyrene granules in the form of beads of
sizes between 0.8 and 1.5 millimeters in diameter and
wherein Ar represents an aromatic radical of the group
containing about 6.5 percent by weight of pentane as
blowing agent was blended with 3 percent by weight of 40 consisting of hydrocarbon and nuclear halohydrocarbon
radicals of the benzene series and R is a member of the
an aqueous emulsion containing poly-dimethyl siloxane
group consisting of hydrogen and the methyl radical, said
liquid in amounts sufficient to coat onto the surfaces of
the beads the siloxan'e in amounts as stated in the fol
alkenyl aromatic polymer containing a volatile organic
?uid selected from the group consisting of saturated ali
with the siloxane emulsion, the beads were dried in air 45 phatic hydrocarbons containing from 4 to 7 carbon atoms
in the molecule, and perchloro?uorocarbons, having a
stream at 40° C. The coated beads were pre—foarned by
molecular weight of at lea-st 58 and boiling at tempera
feeding the same into the bottom section of a vertical
tures below 95° "C. at 760 millimeters absolute pressure,
open tower equipped with a centrally positioned stirrer
dissolved therein in amount corresponding to from 0.05
having a plurality of round radial arms which rotated
between a plurality of stationary round arms projecting 50 to 0.4 gram molecular proportion of the volatile organic
?uid per 100 grams of the alkenyl aromatic polymer, and
inwardly from the inner wall of said tower toward the
said particles of said foamable alkenyl aromatic polymer
center, while at the same time feeding steam into the
having on the surfaces thereof a coating consisting of
bottom section of the tower. The steam upon contacting
‘from 0.0005 to 0.0500 percent by weight of a ?uid poly
the foamalble beads, heats them and causes them to ex
pand and become of lower density. Agitating of the 55 siloxane of the formula R2SiO wherein R is a radical se
lected from the group consisting of the methyl and the
beads by the slow rotation of the stirrer having the round
phenyl radicals and wherein at least 75 percent of the
radial arms causes a lifting action on the beads such
total R radicals in said polysiloxane are methyl radicals.
that the beads of lower density tend to rise to the top of
lowing table. After blending of the polystyrene beads
the body of the beads and are subsequently discharged
from the tower at an upper section when of a desired pre
3. A free-?owing composition comprising discrete par
60 ticles of a foamable thermoplastic styrene polymer con
foamed density. Portions of the pre-foamed polystyrene
sisting of polystyrene, normally susceptible to clumping
and analyzing the alcohol for water by the Karl Fischer
method. Table II identi?es the experiments and gives
polystyrene, and having on the surfaces of the poly
styrene particles a coating of from 0.0005 to 0.0500 per
cent by weight of a ?uid polysiloxane of the ‘formula
into aggregates of a plurality of said particles adhered to
beads were screened to determine the proportion of beads
one another upon expanding by heating, and containing a
which were clumped together as hard agglomerates of a
volatile
organic ?uid consisting of at least one saturated
plurality of two or more individual beads. Other por
tions of the pre-foamed beads were tested to determine 65 aliphatic hydrocarbon having t?rom 4 to 7 carbon atoms
in the molecule, a molecular weight of at least 58 and
the proportion of water adhered to the surface of the
boiling at temperatures below 95 ° C. at 7.60 millimeters
beads. The procedure for determining the amount of
absolute pressure, dissolved therein in amount corre
surface water was to suspend a weighed portion of the
sponding to ‘from 0.05 to 0.4 gram molecular proportion
pre-foamed beads (obtained as they emerged from the
steam pre-foaming tower) in anhydrous methyl alcohol 70 of the volatile organic hydrocarbon per 100 grams of the
the proportion of polydimethyl siloxane, in parts by
RZSiO wherein R is a radical selected from the group
weight per million parts by weight of the beads, em
ployed. The table also gives the proportion of beads 75 consisting of the methyl and the phenyl radicals and
3,086,885
wherein at least 75 percent‘ of the total R radicals in the
polysiloxane are methyl radicals.
4, A composition as claimed in claim 3 wherein the
tween 30 and 60° C. at '7‘60‘anillime-ters absolute pressure
per 100 grams of the polystyrene, and have on the sur
faces thereof a coating of ‘from 0.0005 to 0.0500 percent
foamable polystyrene particles have on the surfaces thereby Weight of a ?uid.polydimethylsiloxa?e
of a coating of from 0.0005 to 0.0500 percent by weight 5
of a ?uid P01y_ dimethylsiloxan6.
5. A composition as claimed in claim 3 wherein the
foamable polystyrene particles contain dissolved therein
from 0.05 to 0.4 gram molecular proportion of a satu-
References Cited in the ?le of this patent
V
UNITED STATES‘ PATENTS
2,744,291
Stas‘tny et a1. __________ __ May 8, 1-956
2,806,509
Bozzacco et a1. _______ __ Sept. 17, 1957
rated aliphatic hydrocarbon boiling at temperatures be- 10
2,861,898
Platzer _____________ _;._ Nov. 25, 1-958